In the insulation of floor drains there is an obvious need for the upper surface of the drain to be flushed with the floor surface so that all liquid may be drained from the floor surface. Prior art drain fittings, especially those molded from plastic or resin materials, include a portion which engages the end of the discharge pipe to effect a leak-proof seal therewith. Generally, this portion comprises an inwardly extending flange in the bore of the drain fitting. In order that the upper end of the discharge pipe may be disposed substantially flush with the inner flange, the length of the discharge pipe must fall within a very narrow tolerance. If that tolerance is not met, the inner flange will rest on the upper end of the discharge pipe but the upper end of the drain will not be flush with the floor surface. The labor and skill involved in meeting the close tolerances of these drain fittings is a significant cost in plumbing installation.
Another problem encountered in the prior art drain fittings is that a substantial amount of solid matter passes through the drain fitting and subsequently lodges in a portion of the discharge pipe, usually the trap immediately below the drain fitting. Drain fittings have commonly been provided with strainers to catch the larger pieces of solid matter carried by the waste water. Often, however, sufficient solid matter passes through the strainer to clog the drain, requiring expensive cleaning and repair of the plumbing system.